Field of the Invention
Embodiments of the invention generally relate to optical fibers having one or more strain isolated fiber Bragg grating sensors.
Description of the Related Art
Optical fibers are often disposed within a tube for protection from damage. In some cases, the optical fibers are inserted by pushing the fibers into the tube with the aid of gas or liquids. For example, the optical fibers may be pushed into a metal tube when manufacturing a fiber in metal tube (FIMT), as described in U.S. Pat. No. 7,024,081, herein incorporated by reference in its entirety.
Multiple fiber Bragg grating (FBG) sensors in an optical fiber inside a metal tube forms a useful optical sensor configuration, such as for measuring temperature. To provide accurate temperature measurements, the FBG sensors typically have to be isolated from strain on the optical fiber. Therefore, it is desirable to have some amount of excess fiber length in the metal tube (also known as overstuff) to reduce strain on the FBG sensors. However, it is difficult to achieve specific amounts of excess fiber length, and often requires placing the optical fiber within the metal tube using very time-consuming and expensive controlled operations.
There is a need, therefore, for techniques for isolating strain from FBG sensors on optical fibers.